Intracellular compartimentalization of Indo-1 and Mag-indo-1: Consequences on intracellular calcium and magnesium sensing and imaging for biomedical applications
Indo-1 and Mag-indo-1 are well known fluorescent probes which consist in two different cages of complexation covalently bound to the same fluorophor. The ionic trap of Indo-1 fit perfectly the size of the calcium ion and its sensitivity is well adapted to the basal concentration of calcium ion in the cytoplasm. Although Mag-indo-1 was designed to complex magnesium, it has been demonstrated that it is a chelator more efficient for calcium than for magnesium. Moreover it has been suggested recently that Fura 2, Indo-1, and Mag-indo-1 migth be partially located inside the membranes of intracellular organelles where the concentration of calcium is expected to be far higher than that of magnesium. All these data question again the use of the simple spectrofluorimetric methods to quantify the cytoplasmic concentration in magnesium. Our studies in solution have confirmed that Mag-indo-1 is a potent chelator for calcium and also demonstrated that the fluorescence spectrum of the calcium-bound Mag-indo-1 is quite similar to that of magnesium-bound Mag-indo-1. Experiments have been carried out with 3T3 cells to quantify the amount of Mag-indo-1 entrapped in the intracellular membranes and its consequences on the monitoring of the intracytoplasmic concentration of magnesium.
